TRACTION FORCES GENERATED BY LOCOMOTING KERATOCYTES

Traction forces produced by moving fibroblasts have been observed as d istortions in flexible substrata including wrinkling of thin, silicone rubber films. Traction forces generated by fibroblast lamellae were t hought to represent the forces required to move the cell forwards. How ever, traction forces could not be detected with faster moving cell ty pes such as leukocytes and growth cones (Harris, A. K., D. Stopak, and P. Wild. 1981. Nature (Lend.). 290:249-251). We have developed a new assay in which traction forces produced by rapidly locomoting fish ker atocytes can be detected by the two-dimensional displacements of small beads embedded in the plane of an elastic substratum. Traction forces were not detected at the rapidly extending front edge of the cell. In stead the largest traction forces were exerted perpendicular to the le ft and right cell margins. The maximum traction forces exerted by kera tocytes were estimated to be similar to 2 X 10(-8) N. The pattern of t raction forces can be related to the locomotion of a single keratocyte in terms of lamellar contractility and area of close cell-substratum contact.